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MECHANICAL SEPARATION                            321
from the furnaces are passed through 6-in. Cottrell pipes under a pressure of 0.22 in. of water. The fume per cu. ft. of gas is 0.000044 Ib. and the velocity of the fume in the Cottrell pipes is 4.9 ft. per sec. The power consumed per 100,000 cu. ft. of gas at a temperature of 206°F. is 1.13 hp.
Developments in recent years with the Cottrell process have continued to show the greatest success with an acid atmosphere or conductor. Sulphuric acid mist can be readily removed and concentrated by the process. In the reduction of phosphate rock in electric or other furnaces, phosphoric acid is recovered by the Cottrell method and is used to saturate phosphate rock giving a superphosphate of high P2O5 content saving the use of sulphuric acid. The Cottrell process does not work with ordinary soot or ash. It has been said that the process has been worked out for the removing of the smoke from railroad round houses but no installation has as yet been put in operation. The engineers of the Research Corporation state they have had some success in such a basic problem as removing the lost carbon from burning natural gas in gas black production. There is now produced but 1 Ib. out of thirty-three available by the present day methods.
The writer has never seen anywhere any statement as to whether as in cata-phoresis certain sorts of particles tend to migrate to the positive pole and others to the negative pole and what effect this would have if the gases were basic or neutral. Nor has he seen any reference to experiments with artificial conducting atmospheres created by introducing with the solids to be separated various gases or vapors. But in this refer to the description of the Feld washer a few pages back.
One effect of the apparatus is to remove the gas adsorbed by the particles as in making water drops coalesce by removing the air envelope surrounding them by electrical discharge and thus permitting internal forces to have full play causing particles to come together, when they will settle more rapidly.
The Cottrell process will not throw down SO2 and it apparently only throws down SOs through the formation and precipitation of sulphuric acid. Water helps on many problems. One use has already been mentioned. It has been stated that zinc fumes with the proper amount of water can be handled at temperatures as high as 600 to 700°F.1 The water must be thoroughly mixed with the fume. Steam also helps in precipitating tin chloride.
The voltage maintained ranges from 30,000 to 100,000. Owing to difficulties in rectifying large amounts of currents the capacity of panel sets ranges from 5 to 50 kw. The Cottrell process can be worked at temperatures where cloth nitration would be out of the question.
PARTS OF THE SHARPLES CENTRIFUGAL. (Numbers refer to figure on p. 309.)
1  Bowl Barrel                            11 Ball Cup Plate
2  Steam Lid                               12 Bowl Spindle
3  Steam Wheel                           13 Speed Indicator
4  Cone Bearing                          14 Bowl Neck
5  Ball Cup Cap                         15 Ball Cup Lock Screw
6  Ball Cup Race                        16 Bowl Shell
7  Ball Cup Shell                        17 Cover Lid
8  Ball Cup Spring                      18 Upper Cover
9  Sight Feed Oiler                      19 Lower Cover 10 Oil Shedder                            20 Bowl Bottom
1 But most makers of zinc oxide believe that wetting fume intended for paint spoils it.    Against this, however, is the practice of one maker, who washes and dries all of his oxide.—EDITOR. 21